The light output of a injection laser in a short (several µm) external cavity has been investigated both experimentally and theoretically. The amplitude modulation ratio of the light output signal reaches maximum where the drive current is below the threshold lasing current. An antireflection coated (ARC) laser diode is useful in increasing the light signal.

The Dynamic Readout performance of a micro-optical head, consisting of a semiconductor laser on a flying slider and a glass substrate disk medium has been examined. An antireflection coated (ARC) laser diode, whose reflectivity facing a medium, is less than 5%, is useful in decreasing signal amplitude fluctuation due to the head-to-medium spacing.

Some sampled servo signal characteristics of an optically switched laser diode (OSL) head are examined. Wobbling signal amplitude increases with bias current and is proportional to the light beam deviation from a track center at around the threshold current corresponding to the low reflection part of the medium. It is confirmed that OSL head tracking can be realized using the sampled servo method.

The optical recording of video signals in real-time and in a high band color mode has been achieved using diode lasers whose light pulse duration is emphasized according to the RF frequency.

Phase change recording with an optically switched laser (OSL) head is realised for the first time. This head consists of a 1.3µm wavelength laser diode monolithically integrated with a photodetector (LD-PD) and a flying slider. The lensless OSL head has a minimum power of 18 mW (1 MHz) for writing information on a 1200 rpm, 130 mm diameter, SbTe based alloy disk. The bit shape and crystalized level are uniform and the readout signals are of high quality.

GaAs-based micromachining is a very attractive technique for integrating mechanical structures and active optical devices, such as laser diodes and photodiodes. For monolithically integrating mechanical parts onto laser diode wafers, the micromachining technique must be compatible with the laser diode fabrication process. Our micromachining technique features three major processes: epitaxitial growth (MOVPE) for both the structural and sacrificial layers, reactive dry-etching by chlorine for high-aspect, three-dimensional structures, and selective wet-etching by peroxide/ammonium hydroxide solution to release the moving parts. These processes are compatible with laser fabrication, so a cantilever beam structure can be fabricated at the same time as a laser diode structure. Furthermore, a single-crystal epitaxial layer has little residual stress, so precise microstructures can be obtained without significant deformation. We fabricated a microbeam resonator sensor composed of two laser diodes, a photodiode, and a micro-cantilever beam with an area of 400700 µm. The cantilever beam is 3 µm wide, 5 µm high, and either 110µm long for a 200-kHz resonant frequency or 50 µm long for a 1-MHz resonant frequency. The cantilever beam is excited by an intensity-modulated laser beam from an integrated excitation laser diode; the vibration signal is detected by a coupled cavity laser diode and a photodiode.